Because of its antibacterial properties, mustard does not require refrigeration; it will not grow mold, mildew or harmful bacteria. Unrefrigerated mustard will lose pungency more quickly, and should be stored in a tightly sealed, sterilized container in a cool, dark place. Mustard can last indefinitely, though it may dry out, lose flavor, or brown from oxidation. Mixing in a small amount of wine or vinegar will often revitalize dried out mustard. Some types of prepared mustard stored for a long time may separate, causing mustard water, which can be corrected by stirring or shaking. If stored for a long time, unrefrigerated mustard can acquire a bitter taste.